1. Field of the Invention
This invention relates to tools which multiply force and, more specifically, to a hand tool which multiplies force by using planocentric hypocycloidal gearing.
2. Related Art
Hand tools which multiply torque are well known. Eight companies worldwide are known to manufacture such devices: Antveks in Russia; Norbar in England; Mito in Japan; Juwel and Walter in Germany; and Geartronics, Central, and Sweeney in the United States.
These companies all utilize a planetary gear design to effect torque multiplication because planetary designs are more compact, and offer significant envelope and weight savings over the single load path of a simple gear mesh. A planetary gearbox transmits power through two or more load paths rather than a single load path characterized by a simple gear mesh. Significantly, none of these companies utilize an planocentric hypocycloidal gear design.
It is well known that planetary gearing is an efficient method of achieving high reduction ratios in minimum space. As shown by Lynwander in Gear Drive Systems Design and Application, Marcel Decker Inc., New York, N.Y., 1983, pp. 6-11, 293-323, the multiple load path of planetary gearing divides the horsepower transmitted among several planet gear meshes and allows the gear size to be reduced significantly compared to parallel shaft designs. In addition, planetary stages can be linked together to achieve high ratios by having the first-stage planet carrier drive the second-stage sun gear and the second-stage carrier drive the third-stage sun gear, etc.
In general, the prior art has established that when high gear ratios (over 15:1) are required, planetary gear systems tend to be more economical, even in relatively small quantities. Lynwander at p. 323. This is because the reduced size of planetary components offset the cost of additional parts in terms of material and the advantages of handling and machining smaller components. For example, using a hardened, ground, helical, parallel shaft gear and using a pinion pitch diameter of 4 inches, a gear pitch diameter of 16 inches, a face width of 4 inches, would require a gearbox envelope of 24.times.12.times.12 inches, and would weigh approximately 650 pounds. However, the equivalent planetary gear set would have a sun gear pitch diameter of 3.5 inches, ring pitch diameter of 10.5 inches, a planet pitch diameter of 3.5 inches, a face width of 3 inches a gearbox envelope of 15 inches in diameter.times.10 inches in length, and would weigh approximately 250 pounds.
The known torque multiplier hand tools :clearly weigh substantially less than the example provided above, as hand tools present fundamentally different size and weight requirements. The Walter Company in Germany provides a torque multiplier of planetary design yielding a 36:1 gear ratio at a weight of approximately 66 pounds (see March, 1987, Walter Company catalog, at p. 10). Achieving the higher ratios, and thus higher torque multiplication, often requires the manufacture and assembly of approximately 41 parts (see March, 1987 Walter Company catalog at p. 12).
Therefore, in the hand tool art, any reduction of the number of parts required for manufacture and assembly, and any reduction of weight would be highly advantageous and significant in terms of material and labor costs. However, a hand tool which achieves a gear ratio of 30:1 in a single stage of reduction and which reduces the total number of parts and weight by at least 50 percent over the torque multiplier hand tools currently employing the planetary gear system is thought to be impossible. Such a hand tool would have an immediate number of applications ;previously not possible due to the reduction in size and would greatly increase the ease with which one person can apply the tool, thereby allowing persons not otherwise able to manipulate larger tools to use the same.
The Ferguson Machine Company has manufactured what is known in the art as the Ferguson Hi-Range speed reducer which comprises two or more pinions driven eccentrically within a stationary ring gear driven either by an eccentric cam on an input shaft or by a cam type input shaft. Power is transmitted when the pinion gears, having drive pin holes, are driven around the stationary ring gear, thereby transferring power to drive pins disposed in the drive pin holes, and thereby rotating and driving an output shaft connected to the drive pins. The drive pin holes in the pinion gears are larger in diameter than the drive pins to allow eccentric movement of the pinion. The Ferguson Hi-Range speed reducer is capable of achieving reductions of up to 360:1 in a single stage. Two diametrically opposed pinion gears: as opposed to a single pinion gear were commonly employed for improved dynamic balance, although additional pinions may be added for additional stability.
The Ferguson Hi-Range speed reducer was used in association with heavy machinery as demonstrated in Ferguson publication BF-100, bulletin PT-67, and catalog 764, which documents are hereby incorporated by reference in their entirety. The focus and application of the Ferguson Hi-Range speed reducer was to reduce the speed of the input shaft. The Ferguson Hi-Range offers efficiency and ease of fabrication, but is only one of many possible planocentric hypocycloidal configurations.
Heretofore, it is thought that planocentric hypocycloidal force multiplication has not been used in association with hand tools.